1. Field of the Invention
The present invention relates to remote staged furnace burner configurations, and more particularly, to the placement of secondary fuel gas nozzles separate and remote from the burners resulting in lower NOX production.
2. Description of the Prior Art
Gas burner furnaces are well known and have been used in reforming and cracking operations and the like for many years. Radiant wall burner furnaces generally include radiant wall burners having central fuel gas-air mixture burner tubes surrounded by annular refractory tiles which are adapted for insertion into openings in the furnace wall. The burner nozzles discharge and burn fuel gas-air mixtures in directions generally parallel and adjacent to the internal faces of the refractory tiles. The combustion of the fuel gas-air mixtures causes the faces of the burner tiles to radiate heat, e.g., to process tubes, and undesirable flame impingement on the process tubes is thereby avoided. Radiant wall burners are typically installed in several rows along a furnace wall. This type of configuration is usually designed to provide uniform heat input to the process tubes from the wall area comprising the radiant wall burner matrix.
Vertical cylindrical furnaces, cabin furnaces and other similar furnaces such as boilers are also well known. Vertical cylindrical furnaces generally include an array of burners on the floor of the furnace that discharge and burn fuel gas-air mixtures vertically. Process tubes are positioned vertically around the burners and adjacent to the cylindrical wall of the furnace whereby heat from the burning fuel gas-air mixtures radiates to the process tubes.
Cabin furnaces and other similar furnaces generally include an array of two or more burners on the rectangular floor of the furnace that discharge and burn fuel gas-air mixtures vertically. Horizontal process tubes are arranged on opposite walls of the furnace which are parallel to the burner array. Additional process tubes can also be arranged adjacent to the top of the furnace. Heat from the burning fuel gas-air mixtures radiates to the process tubes.
More stringent environmental emission standards are continuously being imposed by governmental authorities which limit the quantities of gaseous pollutants such as oxides of nitrogen (NOX) that are introduced into the atmosphere. Such standards have led to the development of staged or secondary fuel burner apparatus and methods wherein all of the air and some of the fuel is burned in a first zone and the remaining fuel is burned in a second downstream zone. In such staged fuel burner apparatus and methods, an excess of air in the first zone functions as a diluent which lowers the temperature of the burning gases and thereby reduces the formation of NOX. Desirably, furnace fuel gases function as a diluent to lower the temperature of the burning secondary fuel and thereby reduce the formation of NOX.
Similarly, staged burner designs have also been developed wherein the burner combusts a primary fuel lean mixture of fuel gas and air and stage fuel risers discharge secondary fuel. The location of the secondary fuel risers can vary, depending on the manufacturer and type of burner, but they are typically located around and adjacent to the perimeter of the primary burner.
While the staged burners and furnace designs have been improved whereby combustion gases containing lower levels of NOX are produced, additional improvement is necessary. Thus, there are needs for improved methods of burning fuel gas and air using burners whereby fuel gases having lower NOX levels are produced.